In our milling section, this article covers information about module milling cutters.
Module Milling Cutters
These are milling cutters used to machine the standard profiles of gear wheels on milling machines. It’s a type of form cutter whose back has been relieved on eccentric lathes, preserving its profile through repeated sharpenings.
In manufacturing, cutting gear grooves according to their number of teeth alone depends on the module value. An accurate profile can only be obtained with a module cutter made for a specific number of teeth. Gear wheels that don’t have the same number of teeth but do have the same module differ from the true profile. Because of this, these two gears won’t mesh properly with each other.
Selecting Module Milling Cutters
To improve meshing and reduce error, these are made as a set and numbered according to the number of teeth they’re meant to cut. This way, a limited group of module cutters can machine gear wheels covering many different tooth counts. (The module is the value obtained by dividing the pitch by the number π (Pi).) Although its unit is millimeters, this isn’t stated in practice.
Normally, an 8-cutter set is used up to module 10. For modules above 10, a 15-cutter set is needed. The markings on one face of the module cutter indicate the module, its number, and the range of tooth counts it can cut.
For example, if a module cutter has the markings: Mod. 1, No. 4, ’21 to 25′, this means: this cutter is the 4th cutter of module 1, and it can cut gear wheels with 21 — 22 — 23 — 24 — 25 teeth. All these details are always clearly marked on module milling cutters by the manufacturer.
On the other face of the cutter, besides the details mentioned above, there’s one of either a = 15° or a = 20°, along with other manufacturing numbers. These degree values are what the milling operator needs. This angle indicates that cutter’s “pressure angle” (contact angle). It thus specifies which pressure angle the involute curve’s construction and manufacture are based on.
Module cutter selection table (above)
The table above shows, for 8-piece and 15-piece cutter sets, which module they belong to and the tooth-count range corresponding to each cutter number. The cutter numbering can also run in reverse — that is, from top to bottom — depending on the preference of the manufacturer.
A module milling cutter mounted on the vertical head of a milling machine. Cutting a spur gear between the dividing head and the tailstock center
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